The present invention relates to a rolling bearing including a rolling element made of steel, and adapted to be used under severe conditions such as high temperature, high speed, high load, high vibration, in for example, a vehicle alternator of an engine auxiliary equipment, a compressor for a vehicle air conditioner, a water pump, etc.
As the rolling bearing of this type, the applicant has already proposed a rolling bearing having a rolling element composed of a steel ball which is imparted with compression residual stress on its surface (Japanese Publication No. JP-A-2000-161362 of unexamined patent application). The rolling element of this rolling bearing is produced in the following manner. After a semi-finished product having a shape close to a finished product has been formed, the semi-finished product is subjected to heat treatments such as annealing and tempering. Then, the heat treated semi-finished product is putted into a rotary container and the rotary container is rotated, and therefore, a surface hardening treatment is applied to the semi-finished product to impart the compression residual stress. Thereafter, a finishing treatment such as polishing is applied to it, thereby obtaining the finished product.
However, in the rolling element of the conventional rolling bearing, after distortion had been given to the interior by subjecting the semi-finished product to the heat treatments, the surface hardening treatment has been conducted to impart the compression residual stress. Accordingly, there has been a fear that when this rolling bearing is employed in a vehicle alternator, exfoliation may occur starting from a stress distorted portion. Moreover, there has been such an anxiety that there are variations in degree of the surface hardening treatment, and when the degree of the surface hardening treatment is too strong, a surface area of the rolling element may become fragile to shorten its rolling life, whereas with too weak degree of the surface hardening treatment, adequate toughness may not be obtained to afford sufficient strength against deformation or crush. In particular, in case where non-metal inclusions such as alumina, titanium nitride, and spherical carbide having high hardness and high elasticity have large particle diameters, occurrence of fragileness and cracks will be promoted, when the degree of the surface hardening treatment is too strong.